Digital circuitry is in widespread use today in many areas such as calculators, counters, electronic watches and many other measurement devices so that many of such devices include digital displays involving integrated circuit techniques. The most common type of such digital displays utilizes seven-segment readout devices for digital numeric indicators. As is well known, by illuminating various combinations of the seven segments, the numbers zero through nine may be formed. Such electrically energizable seven-segment displays may be of any type such as light-emitting diodes, gas discharge tubes, or electroluminescence, etc., the light-emitting diode and incandescent lamp segment being the most common type of digital display in use today.
While such seven-segment displays are extremely reliable, on occasion, one of such segments in an indicator or display may fail as the result of an open circuit or the like. When a segment fails in a display, and is addressed, the failure of the segment to be illuminated results in the indication of an erroneous number. For instance, if the center segment in a seven-segment display burns out, the driving signal to the display for producing the digital display of the numeral "8" becomes a "0" producing an incorrect reading.
In an attempt to alleviate such erroneous readings when a segment fails, one approach has been to generate a blanking signal upon the failure of a segment which is addressed, which signal causes the digital display to go blank thereby indicating that there is a failed segment in the display. However, such a blanking arrangement, while indicating an error, gives no indication of the numeric information which was to be displayed, resulting in a loss of the correct numeric data. Furthermore, to avoid further erroneous readouts, there is no alternative but to discontinue the operation of the display until it can be repaired or replaced.